1. Field of the Invention
The present invention relates to a composition for stripping photoresist, methods of preparing and forming the same, a method of manufacturing a semiconductor device using the composition, and a method of removing a photoresist pattern from an underlying layer using the composition.
2. Description of the Related Art
The process of removing photoresist is an important step in manufacturing a semiconductor device. After completing various processes, such as an etching, ion implantation, etc., photoresist patterns, which typically may be used as a mask in one or more of the aforementioned processes, need to be removed. Additionally, if the photoresist patterns are mis-aligned, these may have to be removed in order to form new photoresist patterns, potentially delaying the manufacturing process. Further, beneath the photoresist patterns may reside one or more layers, such as an oxide layer, aluminum layer, copper layer, polysilicon layer, silicide layer, polyimide layer, etc. Thus, removing the photoresist patterns as soon as possible, and as clean as possible, without harming the underlying layer(s) is necessary in most, if not all, semiconductor device manufacturing processes.
A widely used composition for removing photoresist may include a basic amine compound and a polar solvent as main components, for example. The amine compound may be one of hydroxylamine, diglycol amine, mono-ethanol amine or methyl ethanol amine, for example, and the polar solvent may be water or alcohol.
However, these conventional photoresist removing compositions cannot completely remove polymer components (e.g., polymers) that may be formed during an process of etching the photoresist; thus a pre-treatment process for removing these polymers may be required. The polymers may be produced during plasma etching or reactive ion etching processes which use photoresist patterns as a mask in order to etch an underlying layer of the photoresist patterns, for example. The polymers may be produced through a reaction of the elements C, H, O, etc. in the photoresist patterns with the plasma, such that a polymer is formed on the underlying layer of the photoresist patterns. In particular, when a metal layer is formed under the photoresist patterns, an organo-metallic polymer may be produced. If these organo-metallic polymers are not removed (e.g., polymers remain in a contact hole or a via hole of a semiconductor wafer, for example) a contact resistance might be increased. Accordingly, a pre-treatment process, using a cleaning-intensifying agent for removing polymers, such as a nitric acid solution, for example, may be required prior to applying a photoresist removing composition.
Further, conventional photoresist removing compositions may actually damage an underlying layer. An underlying metal layer could be damaged, since the conventional photoresist removing compositions may include a basic solvent or water. Thus, the underlying metal layer may be subject to corrosion. In order to prevent corrosive damage, a post-treatment process may be performed after the photoresist removing composition is applied, but before performing a post-removal rinsing process. The post-treatment process may include cleaning the photoresist removing composition with isopropyl alcohol, for example.
Since a pre-treating process for removing the photoresist, and a post-removal rinsing process, may both have to be performed in order to remove the photoresist (and polymers related thereto) with a conventional photoresist removing composition, device processing time may be lengthened, potentially lowering productivity. In addition, the application of pre-treating materials and post-treating materials, in addition to the photoresist removing composition, increases production costs. Further, in order to implement pre- and post-treatment processes, corresponding, and different, baths are required, enlarging the size of an apparatus used for removing the photoresist.
In light of the above, Korean Patent No. 10-0335484 (the “484 patent”, registered Apr. 23, 2002) discloses a photoresist removing agent including alkoxy N-hydroxyalkyl alkanamide, a stripping composition for removing photoresist, preparation methods thereof and a method of removing photoresist using the composition. The '484 patent describes a stripping composition having good removing characteristics for removing polymers and photoresist, and which may be used without harming an underlying layer. This composition may include alkoxy N-hydroxyalkyl alkanamide, a polar material having a dipole moment of about three (3) or more, a damage preventing agent and alkanol amine.
The damage preventing agent is added to prevent damage to various layers, such as metal layers, exposed after completing removal of the photoresist. The damage preventing agent may function as a dissolving agent for a reduced organic metal polymer, for example, to prevent corrosion and possible damage to exposed wiring on the surface of an integrated circuit (IC) substrate, for example. A metal oxide layer may be formed on the surface of the exposed wiring pattern, and reacted with a reducing agent so as to be changed into metal ions. During this reaction, a chelating reaction between the damage preventing agent and the metal ions occurs, forming a chelating compound. The surface portion of the exposed wiring pattern may then be covered with stable chelating compounds, preventing corrosion and possible damage to the wiring pattern. Thus, damage to an underlying layer may be prevented due to addition of a damage preventing agent. However, a side-effect of using the damage preventing agent may be a reduced attacking power of the photoresist and a reduced attacking power in removing the polymer formed on the surface portion of the exposed wiring pattern, potentially lowering an overall removing efficiency of a stripping composition containing the damage preventing agent.
After completing fabrication of a semiconductor device such as a chip, a pad and a lead frame may be connected for packaging each chip. The pad may be formed to a thickness of about 10,000 Å. Thus, photoresist patterns for forming the pad may need to be substantially thicker than thicknesses of photoresist patterns used for forming various layers under the pad. Accordingly, even though the photoresist patterns may be removed using an organic stripping composition, polymers in a general shape of a piece of thread, or “thread-type polymers”, may remain, potentially inducing defects in the chip.
If an organic stripping composition and water are not sufficiently mixed, this may also cause the formation of residual thread-type polymers. Further, if the organic stripping composition has a high viscosity, the organic stripping composition might remain, even after a wafer rinsing process is performed, potentially causing further defects.
For example, stripping compositions made by conventional methods and currently available from various companies, when used to remove photoresist, cause the formation of the aforementioned residual thread-type polymers. The results are illustrated in FIGS. 1A–3, which illustrate views of pads containing such residual thread-type polymers.
FIGS. 1A and 1B are views illustrating removing effects of photoresist after removing a photoresist with a prior art stripping composition prepared by a conventional process. FIG. 1A was obtained after applying a stripping composition for the manufacture of 256M DRAM, and FIG. 1B was obtained after applying the stripping composition for the manufacture of 128M DRAM. The applied stripping composition is available from EKC Co., Ltd., and includes hydroxylamine, water, an organic solvent excluding amide, a chelating agent, etc.
As shown in FIGS. 1A and 1B, thread-type residues (defects) were observed. After inspecting 100 pads per wafer, about 20% of the pads for the 256M DRAM contained these defects, and thread-type residues were seen in about 80% of the pads for the 128M DRAM.
FIGS. 2A and 2B are views illustrating removing effects of photoresist after removing a photoresist with another prior art stripping composition prepared by another conventional process. FIG. 2A was obtained after applying a stripping composition for the manufacture of 256M DRAM, and FIG. 23B was obtained after applying the stripping composition for the manufacture of 128M DRAM. The applied stripping composition is available from Dong Woo Fine Chemical Co., Ltd., and includes methoxy N-hydroxyethyl propanamide, water, ethanolamine, catechol (a chelating agent), a damage preventing agent, etc. This stripping composition is disclosed in the '484 patent discussed above.
As shown in FIGS. 2A and 2B, thread-type residues were observed. After inspecting 100 pads per wafer, about 50% of the pads for the 256M DRAM contained these defects, and thread-type residues were seen in about 70% of the pads for the 128M DRAM.
FIG. 3 is a view illustrating removing effects of photoresist after removing a photoresist with a further prior art stripping composition prepared by a further conventional process. FIG. 3 was obtained after applying a stripping composition for the manufacture of 256M DRAM. The applied stripping composition is available from ACT Co., Ltd., and includes amine, water, an organic solvent excluding amide, a chelating agent, etc. As shown in FIG. 3, thread-type residues were observed. After inspecting 100 pads per wafer, about 80% of the pads for the 256M DRAM contained these defects.
Images shown in FIGS. 1A and 3 are obtained using Scanning Electron Microscope (SEM) from Hitachi, Ltd.